1. Field of the Invention
This invention relates generally to production systems wherein workpieces are transferred through a series of equally spaced, linearly aligned work stations which perform a predetermined sequence of operations on the workpieces and, more particularly, to such a system for automatically transferring the workpieces from one work station to an adjacent work station within the system.
2. Description of the Relevant Prior Art
Automated and partly automated systems in which a workpiece is conveyed through a series of work stations which each perform one of a series of operations on the workpiece have rapidly become the norm in manufacturing industries such as the metal working industry. In manufacturing operations such as metal stamping, many separate stamping operations may be required to form the flat sheet of metal into an article such as, for example, a vehicle hubcap. Rather than utilizing several separate presses to stamp the part, it has become the industry standard to utilize a transfer feed press, a single stroke of which is used to perform multiple stamping operations at a plurality of work stations. Typically, a pair of matching dies are disposed above and below each work station. At each stroke of the press, a workpiece will be stamped between each pair of dies. As an individual workpiece moves through the series of work stations, it will be successively stamped by each pair of dies to form the finished product.
Obviously, for efficient operation of such a transfer press, it is critically important that a succession of workpieces be simultaneously transferred from one work station to the next between each stroke of the press. Furthermore, it is often necessary to realign the workpiece with the various die stations of the transfer press. For example, the workpiece may have to be moved linearly in either horizontal direction, or it may be necessary to rotate it. Typically, it is necessary to reorient the workpiece a number of times before forming of the piece is finished. It is readily apparent that some means of rapidly and accurately performing multiple transfers and repositionings must be provided.
One system for performing repetitive workpiece transfer and multiple realignment is a type of walking-beam system which provides transfer rails extending along both sides of a linear axis (x axis) through the work stations upon which the workpieces ride between each adjacent work station. Disposed on the transfer rails are finger grippers for gripping the workpieces. In this type of system, each of the rails is designed for movement along both the X and the vertical axis (Z axis), that is, it both raises and lowers the workpiece and moves it linearly from one work station to another. Furthermore, the finger grippers have associated actuators which permit them to move laterally (along the Y axis), toward and away from the workpieces for engagement therewith and disengagement therefrom. Thus, this design permits the finger grippers to first engage the workpiece by operation of its actuator, then raise the workpiece to the transfer level by actuation of the transfer rails, linearly move the workpiece to the next work station by further actuation of the transfer rails, lower the workpiece, and finally disengage from the workpiece by retracting the finger grippers therefrom so that the press may be operated.
Although such transfer systems are in wide use, they present many disadvantages. For example, many smaller stamping manufacturers and sheet metal die builders do not have transfer presses, which represent a substantial investment, but have a need to duplicate the action of a transfer press for die tryout purposes or short production runs.
Because a standard transfer press supports the rails at each end of the x-axis, rather than in the middle, the rails are typically very heavy, and have a cross section designed to minimize sag. Moving the mass of these rails at production speeds requires large gears and cams, and a massive framework to support the mechanism and provide stability thereto.
Furthermore, standard transfer presses typically have standardized rail positions and permit only two or three different spacings between the rails in the lifted position. Standard transfer presses also have only a limited number of settings along the x-axis and no adjustment of distance of travel in either the up-down or back-forth directions. To exacerbate this problem, the standardized settings are peculiar to each manufacturer and not standardized industry wide. Hence, it would be virtually impossible for one shop to have transfer presses capable of testing or running the many possible combinations of available settings from various press manufacturers.
A further problem with standard transfer presses is the lack of provision for easy removal of the rails for access for purposes of changing the dies. The transfer rails must be longer than the distance between the columns of the press since they also serve to load the workpiece into the press and unload it therefrom. Therefore, elaborate coupling mechanisms are necessary to allow removal of a portion of the rail when the tooling is removed. Die change capability is, therefore, an expensive option and permits rail change or removal only with great difficulty.
As a partial solution to some of these problems, U.S. Pat. No. 4,621,516 to Schafer et al discloses a system wherein the transfer rail does not travel in the linear direction from one station to another. Rather, a secondary rail is mounted thereon and the finger units are in turn mounted on the secondary rail. The secondary rail is designed for reciprocal movement along the X axis between adjacent work spaces. This movement is actuated by a servomotor supported on the secondary rail. The finger units themselves are designed for lateral movement toward and away from the workpiece and are actuated by additional servomotors. In order to raise and lower the workpieces, lift columns are provided upon which the transfer rail is mounted. These lift columns are also actuated by electric servomotors. Hence, according to Schafer's design, only the servomotors which cause lateral movement of the finger units are actually carried along the secondary rails, thus reducing the size of the rails, simplifying the system and making it less prone to failure. Less of the mechanism is actually disposed within the press, thus providing a less obstructed operation thereof. However even with Schafer's improvements, much of the mechanism is still disposed on the transfer rails. Furthermore, existing systems cannot be modified to add these improvements.
It would be desirable to provide transfer rails which are supported in the center to allow a much smaller rail cross section and permit the transfer system to be built to any length. Such a modular system would provide the capability of building longer transfer systems than is presently possible.
It would also be desirable to provide a more flexible transfer system permitting a multiplicity of rail positions and adjustment of finger unit travel in each of the three directions of travel.
Further, it would be desirable to provide an improved, economical system whereby the finger units may be disposed on the rails in relation to the workpiece during die building and tryout, when a transfer press is typically not available. Such a system should also allow greater accessibility to the dies during maintenance and repair by containing the actuator system for the transfer mechanism in separate modules which may be removed, leaving the rails in proper position in relation to the workpiece.
It would also be desirable to provide a system which can be used in a die shop to simulate the action of any transfer press in order to check for proper clearances of moving parts of the dies in relation to the path of travel of the transfer rail, finger units and workpieces without the necessity of actually setting the dies in a transfer press.
It would be highly advantageous to devise a modular system wherein modules may be manufactured in a limited number of sizes and can be used with presses of a variety of sizes and of various configurations, regardless of the direction of feed or of the press design.